Air driven portable sander



June 15, 1954 A. e. LARSON 2,681,042

AIR DRIVEN PORTABLE SANDER Filed Feb. 15, 1952 2 Sheets-Sheet l Inn/anti" Arvicl Larson W June 15, 1954 A. G. LARSON AIR DRIVEN PORTABLE SANDER 2 Sheets-Sheet 2 Filed Feb. 15, 1952 Inn/0125f Arvid GrLarson Patented June 15, 1954 AIR DRIVEN PORTABLE SANBER Arvid G. Larson, Alameda, Calif., assignor to George A. Larson, Rockford, 111.

Application February 15, 1952, Serial No. 271,775

16 Claims.

This invention relates to a new and improved air driven portable sander, the reciprocating motor of which, while especially designed and adapted for use in a portable sander or the like, is applicable wherever similar rapid and fairly powerful reciprocations through a short stroke are desired.

An important object of my invention is the provision of a sander of simple and economical construction and one that is so designed that the thrust of the motor piston is most efficiently transmitted to the sander pad or platen and also with minimum noise and vibration, whereby to reduce fatigue of the operator.

Another important object of my invention is the provision of a motor of the kind mentioned which is of simpler and more economical construction than any I have thus far been aware of and wherein the number of working parts is reduced practically to a minimum, there being only a simple piston and spring pressed valve plungers at opposite ends of the piston, these parts all working in a cylinder provided with ports arranged in a predetermined relationship to the valves and piston.

Another object is to provide a motor of the kind mentioned which is so designed that the yoke to which oscillatory motion is transmitted by the piston in its reciprocation to reciprocate the working part, projects into one side of the cylinder at a mid-point for a direct sliding pivotal connection with the piston intermediate the ends thereof.

The invention is illustrated in the accompanying drawings, in which Fig. l is a horizontal section through a sander taken on the line l-l of Fig. 2 showing the improved air motor of my invention;

Fig. 2 is a longitudinal section in a plane taken on the line 22 of Fig. 1;

Fig. 3 is a cross-section on the line Fig. 2;

Fig. 4 is a plan view of the dust seal plate re moved from the sander, and

Fig. 5 is a plan View of the reciprocable slide and bottom plate, taken on line 5-5 of Fig. 2.

The same reference numerals are applied to corresponding parts throughout these views.

Referring to the drawings, the motor is indivertical cated generally by the reference numeral e I comprises a cylinder 1 in which a single elon gated solid piston 8 is reciprocable. Slidable in the opposite ends of the cylinder 1 are two hollow cylindrical valves 9 and It which are normally urged inwardly by coiled compression springs H and i2, respectively, the latter being backed up by plugs l3 and It, respectively, suitably threaded into the ends of the'cylinder. Intake ports l5 and iii are provided in the cylinder 7 near the opposite ends thereof, and, spaced inwardly from these intake ports are two exhaust ports ll and I8, respectively. Annular internal grooves are preferably provided in the c linder '1' in communication with each of the ports l5-l8, as indicated at 19, for easy inlet of compressed air and easy exhaust thereof circumferentially of the cylinder wall. The two intake ports I! and I?! are interconnected by a longitudinal passage 2! and an air supply pipe 2i has communication with one end of the passage through a counterbore 22. This pipe has a shut-off valve 23 provided on the outer end to control the admission and regulate the flow of the compressed air supplied through a flexible hose 2 that is connected to a suitable source of compressed air supply.

In operation, assuming compressed air is admitted at it, the piston 8 is urged forward moving valve 9 forwardly with it. The forward movement of the piston continues until exhaust port it is uncovered, whereupon the pressure behind piston 8 in the cylinder l drops quickly to a point where the spring !2 is strong enough to move valve it forward, shutting off the intake port it. At this point, valve 9 uncovers intake port it, and, exhaust port it being covered by the piston S, the piston is accordingly moved on the return stroke, duplicating the same sequence with valve Ill, as occurred previously with I valve 9, and so on. The springs H and I? are not strong enough to move the piston 22, especially when the piston 8 is operatively connected with the oscillating yoke member 25, and these springs are, furthermore, light enough in loading in relation to the air pressure employed to permit operation of the valves t and H) in the manner described, the valves remaining retracted under air pressure, as described, until the piston 3 is moved forward far enough to uncover the nearby exhaust port H, or it, as the case may be. The openings 25 in the plugs l3 and it allow free inlet and outlet of air so that there is nothing to interfere with freedom of reciprocation of the valves 53 and It. The opposite ends of the piston are chamfered, as indicated at 8, so as to allow compressed air to enter between the piston and either valve at the start of a stroke. It is obvious that this motor involves substantially a minimum number of working parts, all capable of being manufactured in quantities to the necessary close tolerances at low cost, and that there are no parts apt to show any appreciable wear or apt to break.

The body casting 2'! for the motor 6 is of elongated form, enclosed in a casing 28 which has vent holes provided therein at suitable locations for escape of the air exhausted from the motor during the operation of the sander. In most sanders the air vents are located so as to direct the escaping air toward the surface being sanded, in order to clear it of dust and grit continuously, and the same practice may be followed here. The body casting 21 is suitably secured to the casing 28 by a pair of lugs 29 on the opposite sides thereof into which screws 30 extended from the bot tom plate 3! are threaded, so that the motor is rigid with the casing when the bottom plate 3! and dust seal plate 32 which overlies it are fastened to the casing 28 by means of screws 23 in the recessed bottom portion 34 of the casing. The bottom plate 3! has a rectangular recess 35 in the top thereof under the seal plate 32 and there is a rectangular opening 36 in the plate 3! centrally of this recess. A slide 37 is reciprocable in the recess 35 under the seal plate 32 and has two brackets 38 and 39 riveted to the bottom thereof near the opposite ends projecting downwardly through the opening 36 to make connection with brackets 49 and 4| provided on the opposite end portions of a sander pad or platen 42 on which the sandpaper or other abrasive material is secured, cushioned by a layer of felt or the like applied to the bottom of the platen, as indicated at 43. A third bracket 44 is riveted to the middle portion of the slide 31 and projects downwardly through the opening 36 and has a cylindrical stud 45 on the lower end thereof that is pivotally engaged in a hole 46 in a plate 41 riveted to the middle of the platen 42. Lugs 48 provided on the brackets 38 and 39 are arranged to engage tightly under lugs 49 provided on the brackets 49 and 4! to tie the platen 42 and slide 3! together for reciprocation as a unit. Spring-pressed ball detents 50 caged in the brackets 38 and 35] are arranged to ride into recesses 5| on the brackets 40 and Al when the platen 42 is turned relative to the stud $5 to a position in which its center-line lies in the same vertical plane with the centerline of the slide 3'1. In that way the platen is locked releasably in coupled relation to the slide 31. A cylindrical socket 52 is provided in the top of the bracket 44 and is adapted to receive the spheroidal-shaped drive tooth 53 provided on the lower end of the yoke 25. The latter is pivoted on a cross-pin 54 in a cut-away portion 55 in the middle bottom portion of the body 2! and has a fork 56 on the upper end which is received in the cut-away sides 5'! at the middle of the piston 8, the side portions being cut away so as to leave a fiat-sided connecting web portion 58 between the opposed cylindrical end portions 59 of the piston. The engagement of this fiat-sided web portion 58 in the fork 55 prevents rotation of the piston 8, and the slidable pivotal engagement of the rounded sides 65 of the fork 56 against the flat faces of the cut-away portions 5'! provides a driving connection between the piston and yoke with minimum lost-motion and yet minimum friction losses. The close working fit which the intermediate portion of the yoke 25 has in the opening 55 is enough to make the yoke serve as a closure or dust and dirt seal for the opening to exclude dust and dirt from the cylinder independently of the action of the dust seal plate 32. There is a square hole 6| in the center of the dust seal plate 32 with which the flat ends and rounded bottom of the substantially cylindrical middle bearing portion of the yoke 25 have close sliding engagement. In that way, the likelihood of lubricant provided in the recess 35 for easy reciprocation of the slide 31 is shielded against contamination by dust and grit and wear is accordingly reduced to a minimum. The square opening Si in plate 32 registers with a circular hole 52 provided in the center of the slide 31. Holes 63 in the seal plate 32 register with holes 64 in the bottom plate 3i for escape of exhaust air from inside the casing 28. This air directed downwardly serves to blow the dust and grit off the surface being sanded and tends to reduce the annoyance of this dust rising toward the operators nostrils.

In operation, as the piston 3 reciprocates, the yoke 25 is oscillated and transmits reciprocatory movement to the slide 37 and the attached platen The operation is smooth and quiet largely because of the unique construction of the motor 6 and the direct drive connection provided between the piston 52 and the platen i2, and vibration is reduced by the counteraction of the piston mass always moving in the opposite direction relative to the slide 31 and platen 42. The operator guides the sander over the work by holding the sander using the casing 28 as a handle. The platen 42 may be removed for more convenient replacement of the abrasive material by first turning the same about the stud 45 as a center to disengage the lugs as from lugs t8, after which the platen is, of course, removable from the stud 45. In replacing the platen, the reverse procedure is followed, and, as stated before, when the platen is on center the detents 5B engage in the recesses 55 to lock the platen releasably in the assembled position.

It is believed the foregoing description conveys a good understanding of the objects and advantages of my invention. The appended claims have been drawn to cover all legitimate modifications and adaptations.

I claim:

1. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly.

2. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, compression springs behind said valves normally urging the latter inwardly toward engagement with the piston, and plugs entered in the opposite ends of said cylinder serving as abutments for said compression springs and having openings provided therein for free inlet and outlet of air to the spaces between said plugs and valves.

3. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said. cylinder and adapted to cover and uncover the, exhaust ports alternately, valves slidable as pistons relative to and adapted to cover. and uncover. the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves in.- wardly, the opposite end portions of the piston being chamfered so as to provide annular spaces between the piston and the valves when the piston engages the valves, whereby compressed air may be admitted between the piston and either valve at the start of a stroke.

4. A reciprocating air'motor conr rising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced far-- and uncover the intake ports alternately and n arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly, the cylinder having annular grooves provided' therein in. register with the aforesaid ports for free inlet and free outlet of air annularly of the cylinder wall.

5. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally ur ing the valves inwardly, the opposite end portions of the piston being chamfered so as to provide annular spaces between the piston and the valves when the piston engages the valves, whereby com pressed air may be admitted between the piston and either valve at the start of a stroke, the cylinder ha ving annular grooves provided therein in register with the aforesaid ports for free inlet and free outlet of air annularly of the cylinder wall.

6. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly, the cylinder having an opening in the wall thereof between the exhaust ports, and an oscillating yoke member pivoted in said opening and having one end portion projecting into the cylinder and operatively connected with the piston intermediate the ends thereof and having another end portion projecting in the opposite direction and adapted to be operatively connected with a part to be operated in synchronism with the piston.

'7. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the 6! piston, spring means normally urging the; valves inwardly and means connected with the piston intermediate the ends thereof for transmitting drive.

8. A reciprocating ai'r motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced. farther inwardly from said ends, a piston reciprocable insaid cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to' and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, compression springs behind said valves normally urging the latter inwardly toward en-- gagement with the piston, plugs entered in the: opposite ends of said cylinder serving as abutments for said compression springs and having openings provided therein for free inlet and outlet of air to the spaces between said plugs and. valves, and means connected with the piston ine termediate the ends thereof for transmitting". drive.

9. A reciprocating air motor comprising 9;. cylinder having inlet ports spaced inwardly from theopposite ends and exhaust ports spaced farther. inwardly from said ends, a piston reciprocable in. said cylinder and adapted to cover and uncoverthe exhaust ports alternately, valves slidable as pistons relative to and. adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, spring means normally urging the valves in-- wardly, and an oscillating member pivotally mounted in relation to the cylinder intermediatethe ends thereof for oscillation in the longitudinal plane of the cylinder and operatively connected with said first named piston for oscillation in the reciprocation thereof.

10. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved. by the piston, spring means normally urging the valves inwardly, and an elongated oscillating member pivotally mounted intermediate its ends for oscillation in the longitudinal plane of the cylinder and operatively connected at one end with said first named piston for oscillation in the reciprocation thereof, the other end portion of said oscillating member extending from the cylinder for connection with a part to be operated in timed relation to the reciprocation of said first named piston.

11. A reciprocating air motor comprising a cy1- inder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly, the cylinder having an opening in the wall thereof between the exhaust ports, and an oscillating member pivotally mounted in relation to the cylinder in said opening and operatively connected with said first named piston for oscillation in the reciprocation thereof.

12. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly, the cylinder having an opening in the wall thereof between the exhaust ports, and an elongated oscillating member pivotally mounted intermediate its ends in said opening for oscillation in the longitudinal plane of the cylinder and operatively connected at one end with said first named piston for oscillation in the reciprocation thereof, the other end portion of said oscillating member extending from the cylinder for connection with a part to be operated in timed relation to the reciprocation of said first named piston.

13. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the oppostie ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly, the cylinder having an opening in the wall thereof between the exhaust ports, said first named piston having a reduced portion intermediate its ends movable to and fro relative to said opening in the reciprocation of said piston, and an oscillating yoke member pivoted in said opening and having a forked portion receiving the reduced portion of said piston to operatively connect said piston and yoke member, said yoke member adapted to be operatively connected with a part to be operated in synchronism with the piston.

14. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly, the cylinder having an opening in the wall thereof between the exhaust ports, said first named piston having a reduced portion intermediate its ends movable to and fro relative to said opening in the reciprocation of said piston, and an elongated oscillating yoke member pivoted in said opening and having a forked portion on its one end receiving the reduced portion of said piston to operatively connect said piston and yoke member, the other end portion of said yoke member extending from the cylinder and adapted to be operatively connected with a part to be operated in synchronism with the piston.

15. A reciprocating air motor comprising a cylinder having inlet ports spaced inwardly from the opposite ends and exhaust ports spaced farther inwardly from said ends, a piston reciprocable in said cylinder and adapted to cover and uncover the exhaust ports alternately, valves slidable as pistons relative to and adapted to cover and uncover the intake ports alternately and arranged to be engaged and moved by the piston, and spring means normally urging the valves inwardly, the cylinder having an opening in the wall thereof between the exhaust ports, and an oscillating yoke member pivoted in said opening and having an end portion projecting into the cylinder and operatively connected with the piston intermediate the ends thereof, said yoke member adapted to be operatively connected with a part to be operated in synchronism with the piston.

16. A reciprocating air motor as set forth in claim 9, wherein said oscillating member is pivoted in and substantially closes an opening provided in the wall of said cylinder intermediate the ends thereof and has a portion projecting into the cylinder and operatively connected with the piston.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,119,758 Kings Dec. 1, 1914 1,627,989 Nilson et al May 10, 1927 1,668,966 Kirwin et a1 May 8, 1928 2,272,008 Kehle Feb. 3, 1942 2,324,292 Dremel July 13, 1943 

